Separation of alkenylpyridines from alkylpyridines



Jan. 17, 195s Filed June l2. 1953 United States Patent() SEPARATION FALKENYLPYRIDINES FRM ALKYLPYRIDINES Robert A. Findlay, Bartlesville,Okla., assignor to Phillips Petroleum Company,

This invention relates to the purification of alkenylpyridines. `Inanother aspect this invention relates to the separation and purificationof alkenylpyridines from a mixture of alkenylpyridines andalkylpyridines. In another aspect this invention relates to theseparation and purification of a vinylsubstituted pyridine from amixture of the vinyl-substituted pyridine and the correspondingethylpyridine. In a preferred embodiment, this invention relates to theseparation and purification of Z-methyl- S-vinylpyridine from a mixtureof Z-methyl-S-vinylpyridine and 2methyl5-ethylpyridine The production ofalltenylpyridines, especially vinylpyridines, has recently become ofmuch industrial importance. vinylpyridines can be prepared by thecondensation of formaldehyde with 2-, 4- and 6-methyl substitutedalkylpyridines to form monoethylol pyridines followed by dehydration ofsame by heating to produce corresponding vinylpyridines or substitutedvinylpyridines. A more direct procedure, and one which is probably themost important industrially, is the direct catalytic dehydrogenation ofalkylpyridines to the corresponding alkenylpyridines. Thus, for example,Z-methyl-S-ethylpyridine can be elliciently dehydrogenated to producethe corresponding 2methy1S-vinylpyridine. This can be done, for example,by passing an admixture of from 2 to 15 weights of steam per Weight of2-methyl-5-ethylpyridine, at a temperature Within the range of 1000 to1300" F., at approximately atmospheric pressure, and a space velocity ofl to` 5 liquid volumes Z-methyl-S-ethylpyridine charged per volume ofcatalyst per hour, over a catalyst, exemplified by one composed of 93per cent iron oxide, 5 per cent chromium oxide,` and 2 per centpotassium hydroxide, as described in further detail in the copendingapplication of John E. Mahan, Serial No. 244,469, iiled August 30, 1951.The dehydrogenation effluent contains in addition to hydrogen,principally unchanged 2-methyl-5-ethyl pyridine and2-methyl-5-vinylpyridine product, Also present are small quantities ofpyridine, Z-picoline, -picoline, 2,5-lutidine, 3ethylpyridine and3viny1pyridiue.

Purification of vinylpyridines contained in mixtures produced by theabove described processes or other mixtures presents many difficulties.These arise because of the great ease with which vinylpyridinespolymerize, the closeness of boiling points between vinylpyridine andtheir corresponding ethylpyridines, and the formation of Waterazeotropes and other diflicultly separable fractions on fractionaldistillation of such mixtures. The process of this invention operatesfree of the diliculties from polymerization which are encountered inpurilication of vinylpyridines by fractional distillation as discussedby R. L. Frank, et al., I. E. C. 40, 879.

An object of this invention is to purify alkenylpyridines.

Another object of this invention is to separate and purifyalkenylpyridines from admixture with alkylpyridines.`

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A further object is to separate an alkenylpyridine from admixture withthe corresponding alkylpyridine.

Yet another object is to eiect the separation and purication referred toabove While minimizing polymerization of the alkenylpyridines.

A still further object is to purify 2me=thyl5vinylpyri dine. Furtherobjects and advantages of the invention will be apparent to one skilledin the art from the accompanying disclosure and discussion. l

l have discovered that purification of alkenylpyridines, for example theseparation and purification of alkenylpyridines from alkylpyridines, canbe eliected most satisfactorily by subjecting an admixture of same tofractional crystallization, using anhydrous ammonia as an internalrefrigerant. The alkenylpyridines freeze at higher temperatures than dotheir corresponding alkylpyridines, and thereupon are separable in apure form, thus providing an excellent method for separation andpurification. By an internal refrigerant I mean that anhydrous ammoniais introduced directly into the admixture of alkenylpyridines andcorresponding alkylpyridines and produces refrigeration when saidadmixture is introduced to a zone of reduced pressure to flash theammonia therefrom. This is in contrast to external refrigeration whereinsaid admixture is cooled by external means. The mother liquor resultingfrom the crystallization is subjected to conditions of solventextraction with aqueous ammonia which, due to the greater solubility ofalkenylpyridines in the aqueous ammonia, produces an extract which isenriched in said alltenylpyridines.. The enriched extract is recycled,after being chilled, to the admixture of allienylpyridines andalkylpyridines corresponding thereto to be crystallized and purecrystals of the alkenylpyridine are taken from acrystallization-separation zone.

An important advantage of this process will be apparent immediately tothose skilled in the art in that the problem of polymerization of thealkenylpyridines is minimized, lirst of all, because the separation andpurification process disclosed herein operates at low temperatures,which serves in itself to minimize polymerization. Secondly, ammoniawhich is present throughout my system has a retarding effect againstpolymer formation in alkenylpyridines.

This process of this invention is applicable to alkenylpyridinescontaining at least one allrenyl group having at least 2 carbon atoms,and in a preferred embodiment, to a separation and purication fromalkylpyridines corresponding thereto. By corresponding thereto I meanalkylpyridines having the same number and molecular arrangement ofcarbon atoms. Di-, tri, and tetralkenylpyridines, with the alkenylsubstituents being present in various positions on the pyridine nucleusand wherein the double bond can be in a vinyl group or in the alphaposition of the various possible positions in carbon chains of three andmore carbon atoms in length, can be separated from correspondingalkylpyridines. 2-methyl-5- vinylpyridine and 2-methylS-ethylpyridinemake up one group which it is frequently desired to separate inaccordance with this invention. Other examples of alkenylpyridines whichcan be separated and purified from admixture with alkylpyridinescorresponding thereto in accordance with my invention are,Z-Vinyl-ll-etliylpyridine, Z-ethyl-4-vinylpyridine, 2-vinylpyridine,3-A-propenylpyridine and 2A'pentenylpyridine. Usually the process of myinvention is applied to those alkyl and alkenylpyridines containing atotal of not over 10 carbon atoms in side chains and best results arecustomarily obtained with mixtures containing a monovinylormonopropenylpyridine and the corresponding ethyl or propylpyridine, withor Without one or two methyl groups thereon.

`It is known in the art that mixtures of alkenylpyridines andalkylpyridines, when subjected to cooling,

Patented Jan. 17, 1956 form eutectic mixtures. The eutectic temperatureof the system 2-methyl-5viny1pyridine2methyl5ethyl pyridine is -106.6F., with the freezing point of pure 2-methyl-5-vinylpyridine being 10 F.and the freezing point of `2methylS-ethylpyridine being -94 F. rTheeffective llimits on the temperature for the crystallization ofZ-methyl-S-vinyipyridine according to my process are, therefore, belowF. and above -l06.6 F. A preferred range of temperature, however, isabout *30 F. to about 100 F.

As was stated heretofore, anhydrous ammonia is introduced'into theadmixture of alkenylpyridines and al kylpyridines corresponding theretoto act as an internal refrigerant.` Said admixture containing theammonia is subjected to conditions of reduced pressure thereby loweringthe temperature, to form a crystal magma. Means forvproducing theconditions of reduced pressure are well known to the art, and steam jetsand venturis are herein suggested. Accordingly, this condition ofreduced pressure can be accomplished in a single stage or a plurality ofstages, depending upon the degree of temperature lowering which isdesired.

The crystal magma is transferred to a separation zone which can comprisethe conventional steps for the separation of solid material from liquidmaterial, such as, filtration, centrifuging, or otherwise. In suchconventional separation methods the crystals are treated to removeoccluded mother liquor and the purified product then removed. VApreferred separation zone is a crystal purification column as disclosedby D. L. McKay in the copending application, Serial No. 367,424, ledJuly 14, 1953. This crystal purification column cornprises a meanswhereby a small amount of molten product is supplied to the crystal massas a countercurrent wash liquid thereby producing a purified productwhich is Withdrawn from the bottom of the column. I

An important feature of my invention involves the subjection of themother liquor, resulting from the separation step, to conditions ofsolvent extraction with aqueous ammonia to produce an extract rich inthe alkenylpyridine. Since methods and apparatus for obtaining intimatecontact of two at least partially immiscible liquids are well known tothe art, no detailed description thereof is required. A preferredsolvent ex* traction zone is one involving continuous liquid-liquidcontacting with countercurrent flow'of the solvent. The extraction maybe carried out in a single stage or a plurality of stages. Where amethod of continuous countercurr'ent solvent extraction is used, thefeed mother liquor can enter at an intermediate portion of theextraction tower while the solvent enters near the top of the extractiontower. I use aqueous ammonia for the solvent in the extraction towersince aqueousrannnonia has a greater solubility for alkenylpyridinesthan for alkylpyridines and since ammonia has the attribute of retardingpolymer formation in the alkenylpyridines.

The extract from the solvent extraction zone, which is richV in thealkenylpyridines', is subjected to conditions of reduced pressure toflash therefrom the ammonia and thereby chill the extract to near butabove the freezing temperature of said extract. This condition ofreduced pressure for chilling the extract can be produced in a singlestage or a plurality of stages.

The proportions of the alkenylpyridines and alkylpyridines' present inthe admixture to be separated can vary widely. A preferred embodiment ofmy invention treats the effluent from the dehydrogenation of 2-methyl-S-ethylpyridine to produce Z-methyl-S-vinylpyridine and this eiuent is amixture containing principally about to 40 per cent by weight of2-methyl-5-vinylpyridine, about 60 to 70 per cent by weight of2-methyl-5 ethylpyridine and small quantities of pyridine, 2pico. line,3-picoline, 2,5-lutidine, 3.ethylpyridine and 3- vinylpyridine. Y

The accompanying drawing shows diagr.'tmtnatically one arrangement ofapparatusV elements and iiow of materials therethrough suitable forpracticing my invention in a preferred modification. Various auxiliaryitems of equipment such as valves, pumps, etc., can be supplied by thoseskilled in the art and therefore have not been shown. It will beapparent thatnumerous modifications can be made of the specific detailsshown without departing from the invention.

An admixture of 2-methyl-5-vinylpyridine and 2- methyl-S-ethylpyridineto be separated and from which it is desired to recover purified2metliyl5vinylpyridine is introduced via line 1 and anhydrous ammonia isintroduced to the said admixture via line 3. The admixture containinganhydrous ammonia as an internal refrigerant is passed via line 5 tocooling zone 7, a zone of reduced pressure which chills said admixtureVto form a crystal magma. The crystal magma from cooling zone 7 is passedvia line 9 to the separa- 'tion zone 11 wherein theZ-methyl-S-vinylpyridine crystals are separated from the resultingmother liquor. Occluded mother liquor is washed free from the crystalsand purified2-methyl-5-vinylpyridine is withdrawn from the separationzone y11 via line 13. The mother liquor from the separation zone 11 ispassed via line 15 to solvent extraction zone 17, where liquid-liquidcontacting with the aqueous ammonia solvent in countercurrent flowproduces an extract rich in the 2-methyl- S-vinylpyridine. The extractis passed via line 19 to cooling zone 21 where said extract is subjectedto conditions of reduced pressure thereby chilling said extract to nearbut above its freezing temperature. The chilled extract is passed vialine 23 back to Ythe admixture of 2-me'thyl-5-vnylpyridine andZ-methyl-S-ethylpyridine, thereby enriching said admixture in2-methyl-5-vinylpyridine. Y

The solvent for the extraction process is the aqueous ammonia made up inaqueous ammonia tank 25 to which is added ammonia via line 27 andammoniacontaining water via lines 35 and 57. The aqueous ammonia ispassed Vfrom tank 25 to the solvent extraction zone 17 via line Z9.

The condition of reduced pressure'for coolingrzone 7 is produced by asteam jet 33, in aspirating relation thereto, 'which flashes ammoniafrom said admixture via line 31 and the ammonia-containing watertherefrom is passed via line 35 to the aqueous ammonia tank 25.

The condition of reduced pressure for cooling zone 21 is produced by asteam jet 37, in aspirating relation thereto,V which removes ammoniafrom the extract produced by the solvent extraction zone 17 via line 19to cooling zone 21 and the ammonia-containing water therefrom is passedvia line 41 to an ammonia distillation zone 34. v

The ammonia distillation zone 34 provides for the production ofanhydrous ammonia which is taken overhead via line 47 and aqueousammonia which is taken off via line 44. Water yis removed from theammonia distillationY zone via line 45. The anhydrous ammonia can berecycled to this process where needed, e. g., to be added to theadmixture of 2-methyl-5-vinylpridine and Z-methyl-S-ethylpyridine.Similarly,V the aqueous ammonia can be recycled to the solventextraction zone, or elsewhere in the process, as required.

The raffinate from the solvent extraction zone 17, which is rich inZ-methyl-S-ethylpyridine, is withdrawn from solvent extraction zone 17via line 49 and passed to flash zone 51. Ar condition of reducedpressure is produced in ash zone 51Vby a steam jet 53 which removesammonia from the rainate via line 55 and the ammonia-containing watertherefrom is passed via line 57 to the aqueousV ammonia tank 25.2methyl5ethyl pyridine is withdrawn from ilash zone 51 viarline 59 to berecycled to the purification process, herein disclosed, or to thedehydrogenation process, as desired.

An alternative method of treating the mother liquor from the separationzone' 11 is to remove a portion of said mother liquor as a side streamand recycle it via line 61 to the admixture of alkenylpyridines andalkylpyridines corresponding thereto, passing to the cooling zone 7 vialine 5, and thereby further improve the eiciency of thecrystallization-separation process.

The invention has been described with respect to various preferredembodiments thereof. However, there are numerous variations that can bemade in the details herein given without departing from the invention.In this connection, l wish to emphasize that my process is effective topurify alkenylpyridines, broadly, without regard to the particularmixture in which the alkenylpyridines are found. For example, my processis effective to purify the alkenylpyridine produced by the dehydrationof an alcohol compound referred to earlier herein.

I claim:

l. A process for resolving a mixture of an alkenylpyridine and analkylpyridine corresponding thereto, said alkenylpyridine having atleast one alkenyl group with the double bond in the alpha position andhaving from two to ten carbon atoms in side chains, which comprises,cooling said -mixture with anhydrous ammonia as an internal refrigerantto produce crystals of one of said pyridines and to produce a motherliquor enriched in the other of said pyridines, and separating andrecovering said crystals from said mother liquor.

2. A method for resolving an initial mixture of an alkenylpyridine andan alkylpyridine corresponding thereto, said alkenylpyridine having atleast one alkenyl group with the double bond in the alpha position andhaving from two to ten carbon atoms in side chains, which comprises,cooling said mixture with anhydrous ammonia as an internal refrigerantto crystallize one of said pyridines, separating the resulting crystalsfrom the resulting mother liquor, solvent extracting said mother liquorto produce an extract rich in said pyridine which is crystallized and araiinate rich in the other of said pyridines and adding said extract tosaid initial mixture.

3. A process for resolving an initial mixture of an alkenylpyridine andan alkylpyiidine corresponding thereto, said alkenylpyridine having atleast one alkenyl group with the double bond in the alpha position andhaving from two to ten carbon atoms in side chains, said initial mixtureforming a eutectic mixture and being rich in said alkenylpyridine, whichcomprises, cooling said mixture to crystallize said aikenylpyridine byadding anhydrous ammonia to said mixture and flashing said ammonia underconditions of reduced pressure, separating the resulting crystals ofsaid alkenylpyridine from the resulting mother liquor, solventextracting said mother liquor with aqueous ammonia to produce an extractrich in said alkenylpyridine and a rainate rich in said alkylpyridine,chilling said extract and adding said chilled extract to said initialmixture to enrich said initial mixture in said alkenylpyridine.

4. A process for resolving an initial mixture ofZ-methyl-S-vinylpyridine and Z-methyI-S-ethylpyridine which form aneutectic mixture, said initial mixture being rich in saidZ-methyI-S-Vinylpyridine, which comprises, cooling said mixture withanhydrous ammonia as an internal refrigerant to produce crystals of said2methyl5vinylpyridine and a mother liquor, separating said crystals fromsaid mother liquor, solvent extracting said mother liquor with aqueousammonia to produce an extract rich in 2-methyl5vinylpyridine and arafnate rich in 2-methyl-5-ethylpyridine, cooling said extract andadding said cooled extract to said initial mixturc to enrich saidinitial mixture in said 2-methyl-5- vinylpyridine.

5. A process for the separation and recovery of a vinylpyridine from afeed mixture comprising the reaction products of the catalyticdehydrogenation of an ethylpyridine corresponding to said vinylpyridine,said vinylpyridine having from two to ten carbon atoms in side"`chains,.which comprises, cooling'said feed mixture with anhydrous lammonia asan internal refrigerant to produce crystals of said vinylpyridine and amother liquor, separating said crystals from said mother liquor, solventextracting said mother liquor with aqueous ammonia to produce an extractrich in said vinylpyridine and adding said extract to said feed mixtureto enrich said feed mixture in said vinylpyridine.

6. A process for the separation and recovery of 2-methyl-S-vinylpyridine and Z-methyl-S-etliylpyridine from a feed mixtureof 2-methyl-5-vinylpyridin-e and Z-methyl- S-ethylpyridine, said feedmixture having more than about 30 weight per centZ-methyl-S-vinylpyridine, which comprises, adding anhydrous ammoniaderived as hereinafter recited to said feed mixture, cooling said feedmixture under conditions of reduced pressure in a cooling zone producedas hereinafter described to produce crystals of Z-methyl-S-vinylpyridineand a mother liquor enriched in Z-methyl-S-ethylpyridine, separating andrecovering said crystals of Z-methyl-S-vinylpyridine, solvent-extractingsaid mother liquor in a solvent extraction zone with an aqueous ammoniasolvent derived as hereinafter recited to produce an extract rich in2-methyl-5-vinylpyridine and a raffinate rich inZ-methyl-S-ethylpyridine, separating and recovering said2-methyl-5-vinylpyridine from said rainate, adding said extract to saidfeed mixture, producing said conditions of reduced pressure in saidcooling zone by passing a jet of steam in aspirating relation to saidcooling zone to produce an ammonia-containing water, passing saidammonia-containing water through an ammonia distillation zone to produceanhydrous ammonia and aqueous ammonia, passing said anhydrous ammonia tosaid feed mixture to be added thereto as hereinbefore recited, andpassing said aqueous ammonia to said solvent extraction step as thesolvent therefor as hereinbefore recited.

7. A process for the separation and recovery of 2-methyl-S-vinylpyridine from a feed mixture of Z-methyl-S- vinylpyridineand Z-methyl-S-ethylpyridine, said feed mixture having more than about30 weight per cent Z-methyl- 5-Vinylpyridine, which comprises coolingsaid feed mixture to crystallize the Z-methyl-S-vinylpyridine therein byadding anhydrous ammonia to said feed mixture and subjecting said feedmixture to conditions of reduced pressure in a iirst cooling zone,separating the resulting crystals of 2methyl5vinylpyridine from theresulting mother liquor, passing said mother liquor to a solventextraction zone and therein subjecting said mother liquor toliquid-liquid countercurrent flow solvent extraction with aqueousammonia to produce an extract rich in 2-methyl-5-vinylpyridine and araflinate rich in Z-methyl-S-ethylpyridne, subjecting said extract toconditions of reduced pressure in a second cooling zone to cool saidextract to a temperature near but above the freezing temperature of saidextract, adding the cooled extract to said feed mixture, producing saidconditions of reduced pressure in said cooling zone by passing a jet ofsteam at high velocity in aspirating relation to said cooling zoneswhereby the steam takes up ammonia from said cooling zones and forms anammoniacontaining water, fractionating said ammonia-containing water ina ammonia distillation zone to produce anhydrous ammonia in the overheadand aqueous ammonia in the bottoms of said ammonia distillation zone,passing the anhydrous ammonia thus produced to said feed mixture andpassing the aqueous ammonia thus produced to said solvent extractionzone.

8. The method of claim 7 wherein the said feed mixture of2-methyl5vinylpyridine and Z-methyI-S-ethylpyridine comprises2-methyl-5-vinylpyridine in the range of about 30 to 40 per cent byweight and Z-methyl- 5-ethylpyridine in the range of about 60 to 70 percent by weight and wherein said feed mixture and added extract from saidsolvent extraction are cooled by ashing ammonia therefrom under reducedpressure to a temperature in the range of below 10 F. to above -106.6 F.

comprises 2-methyljf5f-vit1y1pyridine in the range of"about 30 to440 percentl by weight and4 2.-methy15Letliylpyridine in the range of, about 60to 70 per cent by weight and wherein said feed, mixture and addedyextract from said solvent extraction are cooledl by flashingA ammoniaunder redued pressure to a temperature in the range of about 30 F. toabout 10 0" F.

References Cited itlitblqtilel ofthis patentv UNITED .STATES PATENTS;

1. A PROCESS FOR RESOLVING A MIXTURE OF AN ALKENYLPYRIDINE AND ANALKYLPYRIDINE CORRESPONDING THERETO, SAUD ALKENYLPYRIDINE HAVING ATLEAST ONE ALKENYL GROUP WITH THE DOUBLE BOND IN THE ALPHA POSITION ANDHAVING FROM TWO TO TEN CARBON ATOMS IN SIDE CHAINS, WHICH COMPRISES,COOLING SAID MIXTURE WITH ANHYDROUS AMMONIA AS AN INTERNAL REFRIGERANTTO PRODUCE CRYSTALS OF ONE OF SAID PYRIDINES AND TO PRODUCE A MOTHERLIQUOR ENRICHED IN THE OTHER OF SAID PYRIDINES, AND SEPARATING ANDRECOVERING SAID CRYSTALS FROM SAID MOTHER LIQUOR.
 7. A PROCESS FOR THESEPARATION AND RECOVERY OF 2METHYL-5-VINYLPYRIDINE FROM A FEED MIXTUREOF 2-METHYL-5VINYLPYRIDINE AND 2-METHYL-5-ETHYLPRIDINE, SAID FEEDMIXTURE HAVING MORE THAN ABOUT 30 WEIGHT PER CENT2-METHYL5-VINYLPYRIDINE, WHICH COMPRISES COOLING SAID FEED MIXTURE TOCRYSTALLIZE THE 2-METHYL-5-VINYLPYRIDINE THEREIN BY ADDING ANHYDROUSAMMONIA TO SAID FEED MIXTURE AND SUBJECTING SAID FEED MIXTURE TOCONDITINS OF REDUCED PRESSURE IN A FIRST COOLING ZONE, SEPARATINF THERESULTING CRYSTALS OF 2-METHYL-5-VINYLPYRIDINE FROM THE RESULTING MOTHERLIQUOR, PASSING SAID MOTHER LIQUOR TO A SOLVENT EXTRACTION ZONE ANDTHEREIN SUBJECTING SAID MOTHER LIQUOR TO LIQUID -LIQUID COUNTERCURRENTFLOW SOLVENT EXTRACTION WITH AQUEOUS AMMONIA TO PRODUCE AN EXTRACT RICHIN 2-METHYL5-VINYLPYRIDINE AND A RAFFINATE RICH IN2-METHYL-5-ETHYLPYRIDINE, SUBJECTING SAID EXTRACT TO CONDITIONS OFREDUCED PRESSURE IN A SECOND COOLING ZONE TO COOL SAID EXTRACT TO ATEMPERATURE NEAR BUT ABOVE THE FREEZING TEMPERATURE OF SAID EXTRACT,ADDING THE COOLED EXTRACT TO SAID FEED MIXTURE, PRODUCING SAIDCONDITIONS OF REDUCED PRESSURE IN SAID COOLING ZONE BY PASSING A JET OFSTEAM AT HIGH VELOCITY IN ASPIRATING RELATION TO SAID COOLING ZONESWHEREBY THE STEAM TAKES UP AMMONIA FROM SAID COOLING ZONES AND FORMS ANAMMONIACONTAINING WATER, FRACTIONATING SAID AMMONIA-CONTAINING WATER INA AMMONIA DISTILLATION ZONE TO PRODUCE ANHYDROUS AMMONIA IN THE OVERHEADAND AQUEOUS AMMONIA IN THE BOTTOMS OF SAID AMMONIA DISTILLATION ZONE,PASSING THE ANHYDROUS AMMONIA THUS PRODUCED TO SAID FEED MIXTURE ANDPASSING THE AQUEOUS AMMONIA THUS PRODUCED TO SAID SOLVENT EXTRACTIONZONE.